The present invention relates to a valve assembly for drilling systems.
As is known, drilling systems conventionally use perforated rods through which are pumped drilling fluids (drilling muds) adapted to properly control the ground hydrostatic properties and eject from the borehole the bit drilled debris while lubricating and reducing the drilling bit temperature to extend its lifetime and operating efficiency.
Prior drilling system further comprise a driving head and a hydraulic injector assembly for vertically and rotatively driving the drilling rods while pumping said drilling fluids therethrough.
Said prior drilling systems moreover also provide to shut-off the mud injection pumps upon having operatively driven a given drilling rod string, and as a novel drilling rod string must be connected to the driving head.
Conventionally, in this drilling rod withdrawing step, the mud injection pumps are switched off as the whole drilling rod string is withdrawn from the borehole and the string must be removed to recover the remaining rods still present in the borehole.
This operation is dangerous and complex since, as the pumps are switched off and the delivery of the drilling muds through the borehole is stopped, a borehole pressure surge due to a changing of the mud pressure from a dynamic to a static condition occurs, with a possible dangerous accidental and uncontrolled fracturing of the soil.
Moreover, as the mud flow is stopped, also the debris flow to the soil surface is stopped thereby said debris deposit on the borehole bottom, on the back of the drilling bit, thereby the drilling rod battery and related equipments are jammed at the borehole bottom because of the settled down debris.
Both the above situations must be absolutely prevented, because of economic and personnel and environmental safety reasons.